Computations of the trace anomaly of chiral fermions have raised a discussion regarding possible unitarity issues at one-loop in four-dimensional theories involving chiral fermions. This was manifested by the claimed existence of an imaginary CP-violating term in the trace of the energy momentum tensor – the Pontryagin density. We revisit this computation using dimensional regularization and standard Feynman diagram techniques. Working in n dimensions and employing the Breitenlohner-Maison scheme of a strictly four-dimensional γ∗, we show that the parity-odd term vanishes, preserving the reality of the trace and thus the unitarity of the Hamiltonian. We further show that the parity-even contribution is half that of a Dirac fermion.
|Collaboration / Activity||Poster|